The present invention relates to an oscillator scheme, and more particularly to an oscillator apparatus capable of reducing far-out phase noise as well as closed-in phase noise.
In order to reduce closed-in phase noise (e.g. frequency offsets below 100 Hz), a conventional two-pin oscillator such as a conventional Pierces oscillator is arranged to generate and output a smaller voltage signal to a next stage circuit. The smaller amplitude may avoid active devices such as transistors to be affected by nonlinearity effects. However, the smaller amplitude (voltage swing) also means that the device driving capability of the conventional Pierces oscillator is limited. The conventional Pierces oscillator is unable to reduce far-out phase noise (e.g. frequency offsets above 10 KHz). On the other hand, in order to reduce the far-out phase noise (e.g. frequency offsets above 10 KHz), another type of conventional Pierces oscillator is arranged to generate and output a larger voltage signal to a next stage circuit. The larger amplitude improves the device driving capability, but the larger amplitude (voltage swing) unfortunately causes active devices to be affected by the nonlinearity effects. This type of conventional Pierces oscillator is incapable of reducing closed-in phase noise. Thus, both the Pierces oscillators now developed by current industry are unable to reduce far-out phase noise as well as closed-in phase noise simultaneously.